1. Field of The Invention
This invention relates to plastic netting, and more particularly to an extruded bicomponent elastomeric netting having unidirectional elasticity, that is in either the machine direction or the transverse direction.
2. Description of the Related Art
For purposes of the present invention, the terms xe2x80x9ccross machine directionxe2x80x9d and xe2x80x9ctransverse directionxe2x80x9d are synonymous and sometimes simply referred to as xe2x80x9cTDxe2x80x9d, as are the terms xe2x80x9clongitudinal directionxe2x80x9d and xe2x80x9cmachine directionxe2x80x9d, sometimes simply referred to as xe2x80x9cMDxe2x80x9d. However, the term xe2x80x9ctransversexe2x80x9d is sometimes also used to refer to strands which extend in a direction opposite to that of strands previously referred to. The meaning will be clear from the context in any particular instance. Current production elastomeric roll goods, such as scrims, sheets, films, foams, nettings, nonwovens, fibers, threads and the like are basically isotropic, exhibiting essentially the same properties in all directions of their two dimensional plane. However, in many applications, elastomeric properties are desired in only one direction, while elastomeric properties in the other direction are unnecessary or even detrimental to product functionality. Although numerous patents exist describing netting, woven and non-woven fabrics, meshes and chain nets with bicomponent materials or unidirectional elasticity or netlike articles, they do not provide any suggestion to modify the prior art such as is done in the present invention with respect to extruded plastic net. Existing technology does not include an extruded bicomponent elastomeric netting with unidirectional elasticity which may be manufactured more economically than most conventional elastomeric netting on the market.
Nets, wovens and nonwoven reinforcements made of more than one material are disclosed in U.S. Pat. No. 4,636,419 to Madsen, U.S. Pat. No. 4,241,123 to Shih, and U.S. Pat. No. 4,460,633 to Kobayashi et al. In addition, a netting die fed by two separate polymer streams is disclosed in U.S. Pat. No. 3,791,784 to Arechavaleta.
U.S. Pat. No. 4,636,419 issued to Madsen et al on Jan. 13, 1987 discloses a xe2x80x9cNet and Method of Producing Samexe2x80x9d which employs a combination of side by side extrusion streams, transversal embossment, and splitting to produce netting composed of a regular array of longitudinal ribbon-formed continuous polymer filaments and a regular array of transverse stems or strands of a different polymer matter. It is disclosed that the use of two different polymer substances in two directions affords netting of interesting and unusual properties (col. 2, Ins 12-25 and 30-31). In Example One, the cross machine component comprises Nylon 6 and the machine direction component comprises polypropylene (col. 11, Ins. 13-31). It is disclosed that elastomeric netting may be prepared by the method of this patent, and preferred materials as well as a suitable application for such netting is disclosed (col. 9, In. 67 through col. 10, In. 7). Unidirectional elasticity in net as-extruded is neither disclosed nor suggested.
U.S. Pat. No. 4,241,123 issued to Shih on Dec. 23, 1980 discloses non-woven netting wherein a first group of melting monofilaments are die extruded and a second group of monofilaments or a yam is crossed, pressed, and welded to form a welded plastic netting (col. 3, Ins. 8-12). Unidirectional elasticity is not disclosed.
U.S. Pat. No. 4,460,633 issued to Kobayashi et al on Jul. 17, 1984 discloses a nonwoven reinforcement for resinous composites made of bundles of non-twist or soft twist yams as warps on both sides of bundles of non-twist or soft twist yams as wefts, warps and wefts being bonded by an adhesive agent impregnated into the wefts. This invention differs from the present invention in that it does not suggest unidirectional elasticity, having flexure no different from that of a woven fabric.
U.S. Pat. No. 4,980,227 issued to Sekiguchi et al on Dec. 25, 1990 discloses a stiff, netlike sheet of heat bonded five layer and three layer polyolefin yams which exhibits retention of its sheet-like shape due to its stiffness. Although heat bonding of polyolefin materials is mentioned, neither an extruded net nor the use of another material to produce unidirectional elasticity is disclosed or suggested.
U.S. Pat. No. 3,791,784 to Arechavaleta discloses an extrusion die fed by two separate polymer streams. Although Arechavaleta suggests that two different materials may be extruded, it is not suggested that the die be used to produce a resulting netting structure which will possess good strand to strand bond, uniform transverse direction strand spacing, or a high transverse direction packing density, i.e. transverse direction strandcount, nor is a net having unidirectional elasticity suggested. In particular it is not suggested that netting strands made of two basically incompatible resin groups, such as polyolefins and styrenic block copolymers, can provide a good bond with the associated desirable properties. Differences in polymer compatibility, rheology, processing melt history, melt temperatures and the like contribute to the expectation of a poor strand to strand bond as compared to a situation in which one polymer component is used for the two melt streams.
Fabrics, meshes, chain nets, and support materials with elastic properties are disclosed in U.S. Pat. No. 4,107,371 issued to Dean, U.S. Pat. No. 4,673,015 issued to Andreasson, U.S. Pat. No. 4,728,565 issued to Fontana, U.S. Pat. No. 4,469,739 issued to Gretzinger, and U.S. Pat. No. 4,351,872 issued to Brosseau et al. These products are expensive to produce, and are significantly different from a netting product.
U.S. Pat. No. 4,107,371 issued to Dean on Aug. 15, 1978 discloses a fabric woven of plastic-coated yam and polymer strands that is relatively stiff in one direction and relatively flexible in the other direction. This differs from the present invention in that it does not disclose, teach or suggest making an extruded net from two different polymers.
U.S. Pat. No. 4,351,872 issued to Brosseau et al on Sep. 28, 1982 discloses a unidirectional stretch mesh laminate used in an orthopaedic traction hamess. A commercially available DuPont unidirectional stretch mesh is discussed at col. 3, Ins. 12-18 as a component of the invention. No patent was found disclosing said mesh.
U.S. Pat. No. 4,469,739 issued to Gretzinger on Sep. 4, 1984 discloses an oriented woven furniture support material made in part from an elastomer monofilament and in part from synthetic or natural yarn. Unlike the extruded bicomponent elastomeric netting of the present invention, this material is woven, and is not completely plastic in composition.
U.S. Pat. No. 4,673,015 issued to Andreasson on Jun. 16, 1987 discloses a chain net which may include links of elastically deformable material. is suggested that although warp and weft strands are usually made of links of similarly elastic material, the weft strands may alternatively be made of other material (col. 2, Ins. 49-64). Although unidirectional elasticity is suggested, this patent does not disclose an extruded net.
U.S. Pat. No. 4,728,565 issued to Fontana on Mar. 1, 1988discloses an elastic support member for supporting stuffing of furniture pieces comprising an elastic net or belt formed of a net or honeycomb fabric or a woven fabric comprised of rubber threads arranged in at least one of the transverse and longitudinal directions. This patent is an improvement of Italian Patent No. 955,134. Although the appearance of rubber threads in at least one direction suggests unidirectional elasticity, this patent neither discloses nor suggests an extruded net as in the presently disclosed invention.
The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is xe2x80x9cprior artxe2x80x9d with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. xc2xa71.56(a) exists.
The present invention is an extruded bicomponent elastomeric netting having unidirectional elasticity. It is economical to produce. The bicomponent netting of the present invention may be produced by an extrusion die fed by two separate polymer streams. Such a netting is a non-woven employing a relatively non-elastic strand material in one direction and a relatively elastic transverse strand material in the opposite direction. Any combination of resins with an elastomeric resin blend may be used, as long as the two types of resin strands are compatible from processing and rheological standpoints. For example the strands of the two resin streams should show good joint bond strength. The net may comprise preferably a non-elastic material such as a polyolefin in the machine direction and an elastic material in the cross machine direction. A product with reverse strand distribution may also be produced, with the elastic material in the machine direction and the non-elastic material in the cross machine direction. It was unexpectedly found that polyolefins and styrenic blok copolymers, two basically incompatible polymers, possess good bond strength. For the purposes of this invention, that combination represents a preferred embodiment of the invention. That preferred embodiment of the invention employs an elastic material of a styrenic block copolymer resin such as is commercially available under the Kraton(copyright) brand from Shell Oil Company, Houston, Tex. or the Vector brand which is available from Dexco Polymers, a Dow/Exxon partnership, of Plaquemine, La. The non-elastic strands are preferably in the machine direction in this preferred embodiment and may be oriented. Of course, the opposite arrangement of strands may be used according to this invention.